i7-5820k Core temps MUCH higher than CPU Temperature. Is it safe?

mordhau5,

On behalf of the Moderator Team, welcome to Tom's!

I'm sure your custom water cooling is solid, and Liquid Ultra is a fantastic TIM, so let's rule out those variables.

Here's the normal operating range for Core temperature:

80C Hot (100% Load)
75C Warm
70C Warm (Heavy Load)
60C Norm
50C Norm (Medium Load)
40C Norm
30C Cool (Idle)
25C Cool

Core temperatures in the mid 70's are safe, so you need to keep it under 80C.

Your high Core temperatures are being driven strictly through your Core voltage being much too high, but there's also a few common misconception we need to clear up, which always create considerable confusion in processor temperature topics.

(1) Your i7 5820K is 22 nanometer microarchitecture. As such, the maximum recommended Vcore is 1.3 volts. 1.45 is potentially destructive to you processor with respect to electromigration. Also, as has already been discussed, X-99 motherboards are vulnerable to high TDP (140 Watts) CPU's as a result of high Vcore due to overclocking, which causes even higher Wattage and amperage to be drawn through the power planes within the layers of the motherboard to feed devices such as VRM's.

Use "Core Temp" to monitor your processor's Power (Watts) and you'll see what I mean - http://www.alcpu.com/CoreTemp

(2) Do NOT run any versions of Prime95 later than 26.6. Here's why:

Core i 2nd through 6th Generation CPU's have AVX (Advanced Vector Extension) instruction sets. Recent versions of Prime95, such as 28.9, run AVX code on the Floating Point Unit (FPU) math coprocessor, which produces unrealistically high temperatures. The FPU test in the utility AIDA64 shows similar results.

Prime95 v26.6 produces temperatures on 3rd through 6th Generation processors more consistent with 2nd Generation, which also have AVX instructions, but do not suffer from thermal extremes due to having a significantly larger Die.

Please download Prime95 version 26.6 - http://windows-downloads-center.blogspot.com/2011/04/prime95-266.html

Run only Small FFT’s for 10 minutes.

Your Core temperatures will test 10 to 20C lower with v26.6 than with v28.9, not to mention the Wattage.

Keep in mind that Prime95 Small FFT's is a steady-state 100% workload which produces steady-state temperatures. On the other hand, RealBench is a fluctuating workload which produces fluctuating temperatures, so it's normal to see your Core temperatures fluctuate when running RealBench.

(3) Let's get our terminology straight; there is no "Socket" temperature for Intel processors. "Socket" applies to AMD processors.

The term "CPU" temperature is synonymous with Intel's "Tcase" specification, which is a laboratory thermocouple measurement sampled on the surface of the IHS. The last processors that actually had an analog thermal diode to measure "CPU" temperature was socket 1366 back in the day of the 1st Gen i7 920.

Also, Core temperature is 5C higher than the Tcase specification (CPU temperature) due to the proximity of the DTS sensors to the heat sources, which originates in the "hot spots" at the transistor junctions within the Cores. As such, the following comments offered above by Multipack are incorrect:


Much to the contrary, the hottest processor temperatures are always Core temperatures, which are indeed most relevant.

Further, "water" or liquid temperature in your loop has no relationship to "Package" temperature, which is defined as the hottest Core.

(4) Don't depend on SpeedFan to correctly assign labels to devices. This is often the cause of much confusion when using SpeedFan. Don't get me wrong; it's a great utility that's highly configurable which I've used on various rigs for many years, but it has a bit of a challenging learning curve to get it set up correctly so that the labels accurately correspond to the appropriate devices. If SpeedFan is telling you there's a "CPU" temperature, there actually isn't one; it simply misused the term "CPU" to assign a temperature to a device such as VRM's.

(5) Intel groups your i7 5820K as a "High-End" processor - http://ark.intel.com/products/family/79318/Intel-High-End-Desktop-Processors#@Desktop

As such, High-End processors do not use TIM between the Die and the IHS; they still use Indium solder due to the need to efficiently dissipate heat from high TDP processors such as the 140 Watt i7 5820K, so you can dispose of this as a variable. Other than High-End processors, 2nd Gen Sandy Bridge were the last processors to all use solder due to the cost of Indium, which is a rather expensive and toxic exotic material. Again, other than High-End processors, 3rd Gen and later now use a Dow Corning TIM.

The bottom line is that you need to reduce your Vcore to something closer to 1.3. When tweaking your processor near it's highest overclock, keep in mind that for an increase of 100 MHz, a corresponding increase of about 50 millivolts (0.050) is needed to maintain stability. If 75 to 100 millivolts or more is needed for the next stable 100 MHz increase, it means your processor is overclocked beyond it's limits.

With high TDP air or liquid cooling you might reach the Vcore limit before 80C. With low-end cooling you’ll reach 80C before the Vcore limit. Regardless, whichever limit you reach first is where you should stop, declare victory and have a beer.

Remember to keep overclocking in perspective. For example, the difference between 4.5 GHz and 4.6 Ghz is only 2.2%, which has no noticeable impact on overall system performance. It simply isn’t worth pushing your processor beyond recommended Core voltage and Core temperature limits just to squeeze out another 100 MHz.

If you'd like to get yourself up to speed on this topic, then you might want to read this Sticky: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

CT